This invention relates to edible food casings, especially for sausages, which are dyed with an edible dyestuff, and to a process for the manufacture of such casings.
The invention is an improvement in, or modification of, that forming the subject of co-pending application Ser. No. 340,776, filed March 13, 1973, now abandoned.
Edible food casings made of a skin fiber composition of animal origin (collagen) are known especially for sausages. Such casings are being used increasingly for the production of frankfurters and Vienna sausages, and their manufacture is described, for example, in German Pat. No. 972,854. Such collagen sausage casings range from practically colorless to pale yellow. In sausages where the casing is intended to be consumed, and especially in the case of the various scalding sausages, such as bockwurst, an increasing consumer preference towards a strongly colored sausage has become evident. Thus in some countries, such as USA, France and Great Britain, certain sausages, such as the well-known "hot dogs" are marketed dyed red. The red dyeing is effected together with the scalding or boiling process, by surface dyeing of the sausage casing, through addition of the dyestuff to the bath in which the filled sausage is scalded or boiled.
Such a method of dyeing has several disadvantages: First, uniform dyeing can be obtained only with great difficulty. The casing shows regions which are dyed more weakly or not at all, depending on how close together the sausages were laying and how adequately they have been wetted by the dyestuff liquor. Furthermore, the dyestuff tends both to bleed out and also to migrate into the sausage material. In spite of using the same dyestuff concentration, completely identical dyeing of successive batches is never achieved.
It has also been proposed to dye artificial sausage casings made of extrudable material which swells in water by dissolving edible dyestuffs soluble in fat or oil and distributing the resulting solution in the form of a "fat-in-water" emulsion in the raw material of the casings before they are shaped (Canadian Pat. No. 906 716, TEE-PAK).
In practice, dyed sausage casings produced in this manner have the disadvantage that during the scalding sausage preparation, under the action of hot air, steam, and scalding water, considerable portions of the dyed fats embedded in the casing material come into contact with the largely fatty sausage composition and color it. The result is a substantial disappearance of the coloring of the sausage casing and an undesired transfer of the dye to the periphery of the sausage material.
In said application Ser. No. 340,776, it is proposed to dye a sausage casing of edible material such as collagen or alginate, with an edible dyestuff, which represents a significant improvement in composition with the known dyed sausage casings as regards uniformity of dyeing and fixing the dye in the casing. The sausage casings according to said Ser. No. 340,776 are dyed with an edible, e.g. legally permitted, dyestuff (primarily a water-soluble dyestuff).
A proposed in the copending application, the dyeing may be effected by adding the dyestuff to the composition before extruding the tube, or by immersion of the tube, or by spraying the extruded tube with an aqueous dyestuff solution. Fixing the dyestuff on or in the casing may be effected, in the case of dyeing the extruded sausage casings, by employing as the dyes, substances which are cross-linkable under the action of heat, and/or the action of hardening or tanning agents. Such agents include proteins, cellulose, cellulose derivatives, pectins, alginates and structurally similar substances. Examples of proteins which may be used include gelatin, casein, and collagen. Swellable cellulose derivatives such as methyl cellulose, ethyl cellulose, are also suitable, as are gum arabic and guar gum as hardening or tanning agents similar to pectin. The quantity of any such substance added may be from 0.1 to 2% based on the aqueous dye solution. The dye baths produced in this manner may be regarded as dyed colloidal solutions of the proteins or polymeric carbohydrates. By adding tanning agents such as, for example, glutaraldehyde, glyoxal, or aluminium salts, the dyes can be cross-linked with the base substance of the tube, e.g. collagen. A certain degree of cross-linking and water-resistance can also be produced without using hardening or tanning agents, by exposure to hot air at 70.degree. to 105.degree. C for 4 to 10 hours.
If the dyestuff is added to the composition before tube formation, a very effective method of fixing the dyestuff consists of embedding it in a hydrophobic substance, for example, a fat, and then emulsifying it in this form into the composition to be extruded, preferably collagen. This method is particularly advantageous for water-soluble food dyestuffs.
As described in the said Ser. No. 340,776 a further improvement of the efficiency of the dyestuff, in conjunction with excellent fixing, is obtained if the water soluble dyestuff is first of all applied to a carrier and the dyed carrier is then surrounded by a hydrophobic encapsulating substance. Suitable dyestuff carriers comprise all insoluble, swellable or non-swellable materials which are edible or harmless. Preferably, a white or colorless carrier substance is used so that the color shade is not changed by the intrinsic coloration of the carrier. Examples of suitable carrier materials include cellulose and cellulose derivatives in the form of fibers or powders, starch powders, collagen powders and casein powders. Of course, mixtures of such materials can also be employed.
Advantageously the carrier, which consists, for example, of particles of a finely ground cellulose powder, is dyed with a relatively concentrated solution of the dyestuff in a hydrophobic encapsulating agent and then dried. Possible hydrophobic encapsulating substances comprise all those oils and fats which are customarily used in the foodstuff field, for example synthetic glyceride mixtures, sunflower seed oil, beef fat and lard. High-melting fats and waxes can also be used such as, for example, beeswax and paraffin, alone or mixed with the other fats and oils.